Division of Cancer Biology at State Key Laboratory for Diagnosis & Treatment of Infectious Diseases, First Affiliated Hospital, Zhejiang University College of Medicine, Hangzhou 310003, China.
Mol Cancer. 2011 May 28;10:66. doi: 10.1186/1476-4598-10-66.
Epithelial to mesenchymal transition (EMT) occurs during cancer cell invasion and malignant metastasis. Features of EMT include spindle-like cell morphology, loss of epithelial cellular markers and gain of mesenchymal phenotype. Activation of the RON receptor tyrosine kinase by macrophage-stimulating protein (MSP) has been implicated in cellular EMT program; however, the major signaling determinant(s) responsible for MSP-induced EMT is unknown.
The study presented here demonstrates that RSK2, a downstream signaling protein of the Ras-Erk1/2 pathway, is the principal molecule that links MSP-activated RON signaling to complete EMT. Using MDCK cells expressing RON as a model, a spindle-shape based screen was conducted, which identifies RSK2 among various intracellular proteins as a potential signaling molecule responsible for MSP-induced EMT. MSP stimulation dissociated RSK2 with Erk1/2 and promoted RSK2 nuclear translocation. MSP strongly induced RSK2 phosphorylation in a dose-dependent manner. These effects relied on RON and Erk1/2 phosphorylation, which is significantly potentiated by transforming growth factor (TGF)-β1, an EMT-inducing cytokine. Specific RSK inhibitor SL0101 completely prevented MSP-induced RSK phosphorylation, which results in inhibition of MSP-induced spindle-like morphology and suppression of cell migration associated with EMT. In HT-29 cancer cells that barely express RSK2, forced RSK2 expression results in EMT-like phenotype upon MSP stimulation. Moreover, specific siRNA-mediated silencing of RSK2 but not RSK1 in L3.6pl pancreatic cancer cells significantly inhibited MSP-induced EMT-like phenotype and cell migration.
MSP-induced RSK2 activation is a critical determinant linking RON signaling to cellular EMT program. Inhibition of RSK2 activity may provide a therapeutic opportunity for blocking RON-mediated cancer cell migration and subsequent invasion.
上皮间质转化（EMT）发生于癌细胞侵袭和恶性转移过程中。EMT 的特征包括梭形细胞形态、上皮细胞标志物丢失和间充质表型获得。巨噬细胞刺激蛋白（MSP）激活 RON 受体酪氨酸激酶与细胞 EMT 程序有关；然而，导致 MSP 诱导 EMT 的主要信号决定因素尚不清楚。
本研究表明，RSK2，Ras-Erk1/2 通路的下游信号蛋白，是将 MSP 激活的 RON 信号与完全 EMT 联系起来的主要分子。使用表达 RON 的 MDCK 细胞作为模型，进行了基于纺锤形的筛选，在各种细胞内蛋白中确定 RSK2 是 MSP 诱导 EMT 的潜在信号分子。MSP 刺激使 RSK2 与 Erk1/2 分离，并促进 RSK2 核转位。MSP 以剂量依赖的方式强烈诱导 RSK2 磷酸化。这些效应依赖于 RON 和 Erk1/2 的磷酸化，这一过程被 EMT 诱导细胞因子 TGF-β1 显著增强。特异性 RSK 抑制剂 SL0101 完全阻止了 MSP 诱导的 RSK 磷酸化，从而抑制了 MSP 诱导的纺锤形形态和 EMT 相关的细胞迁移。在几乎不表达 RSK2 的 HT-29 癌细胞中，MSP 刺激下强制表达 RSK2 会导致 EMT 样表型。此外，L3.6pl 胰腺癌细胞中特异性 siRNA 介导的 RSK2 沉默而非 RSK1 沉默显著抑制了 MSP 诱导的 EMT 样表型和细胞迁移。
MSP 诱导的 RSK2 激活是将 RON 信号与细胞 EMT 程序联系起来的关键决定因素。抑制 RSK2 活性可能为阻断 RON 介导的癌细胞迁移和随后的侵袭提供治疗机会。
